1. Technical Field
The present invention relates to a state judging device and a control device of a secondary battery, and in particular, to a device which judges a change in capacity balance in a secondary battery in which a capacity of one of a cathode (positive electrode) and an anode (negative electrode) is regulated.
2. Related Art
A secondary battery such as a nickel-metal hydride battery and a lithium ion battery is used as a power supply for supplying electric power to a drive motor or the like of an electric vehicle and a hybrid electric vehicle.
As the nickel-metal hydride battery, in order to reduce size, weight, and cost of the battery while avoiding an increase in an internal pressure of the battery, a structure is known in which a capacity of an anode is set to be greater than a capacity of a cathode by a predetermined margin capacity, at the time of charging.
JP 2004-273295 A discloses a sealed-type nickel-metal hydride secondary battery comprising a cathode which includes nickel hydroxide as a cathode active material, and an anode which includes a hydrogen absorbing alloy as an anode active material, which has a charge reserve CR which is an excessive capacity which is provided in advance and which is in a non-charged state when charging of the cathode is completed, a discharge reserve DR which is an excessive capacity which is provided in advance and which is in a charged state when discharging of the cathode is completed, and which has a greater capacity than a theoretical capacity of the cathode.
However, in the design of the secondary battery, even if an anode having a greater capacity than the theoretical capacity of the cathode is employed as in JP 2004-273295 A, a capacity balance between the cathode and the anode may change due to aging deterioration of the secondary battery. In the related art, such a change in capacity balance between the cathode and the anode due to the aging deterioration is not considered, and the internal state related to the capacity balance of the secondary battery can only be known by destructing the secondary battery and inspecting with single electrode (capacity measurement).
Even when the capacity of the anode is greater than that of the cathode at the initial state, as a result of the change of the capacity balance due to the aging deterioration, there may be cases where the capacity of the cathode becomes greater than that of the anode, which is an opposite state than at the time of manufacturing. In this case, the capacity (SOC)-voltage curve also changes, and as a result, an error occurs in an SOC estimation value based on the voltage of the secondary battery and the secondary battery cannot be accurately controlled to be charged or discharged.